The thermal and catalytic cracking of several plastic wastes (polypropylene, polystyrene, polystyrene−polybutadiene) dissolved in refinery LCO has been studied in a riser simulator, under operating conditions (catalyst, temperature, contact time, C/O ratio) that are similar to commercial FCC units. The results of the product distribution show the interest of this strategy, which may be integrated into refinery operation for large-scale tertiary exploitation of plastic wastes.